1. Field of the Invention
The present invention relates to dental titanium castings, in particular to dental castings produced by casting titanium alloys containing a specified quantity of vanadium and aluminium.
2. Description of the Prior Art
Titanium and its alloys have superior physical characteristics, such as lightweightness and increased mechanical strength, and superior chemical corrosion resistance, so that they have been recently used in flying machines, space rockets, chemical plants and the like frequently, and they have a superior wetting property, so that they have been frequently used as a living body material such as dental making-up substance. In particular, Ti-6Al-4V alloy (titanium alloy containing aluminium at a ratio of 6% by weight and vanadium at a ratio of 4% by weight) is well known as a titanium alloy for used in flying machines. This alloy has physical characteristics superior to those of pure titanium, as shown in Table 1.
TABLE 1 ______________________________________ pure titanium Ti--6 Al--4 V ______________________________________ Tensile strength 35-50 91-95 (Kgf/mm.sup.2) Elongation (%) 23 15 Hardness (Hv) 110-150 300 ______________________________________
Accordingly, taking notice of superior physical characteristics of this Ti-6Al-4V alloy, it has been published in many papers that it is used as a living body material. Also in the dentistry, it has been intended to use this alloy for dental making-up substances such as inplants and metallic beds.
However, in the above described cases of flying machines and the like, since the parts are generally large-sized, they can be produced by a method other than the casting, such as the forging, but in the cases of small-sized and complicated in shape parts, such as dental making-up substances, they are difficult to produce by methods other than the casting. However, in the case where a Ti-6Al-4V alloy is cast, castings merely subjected to the casting cannot reproduce physical characteristics of the original alloy. That is to say, they are hard and brittle. Accordingly, in order to use them in dentistry, a remarkably troublesome after-treatment, such as a heat treatment under a high vacuum atmosphere after the casting, is required, whereby they have never been practically used as dental castings.